Automatic fuel ignition system

ABSTRACT

An automatic fuel ignition system includes an ignition circuit having an ignition transformer with a primary winding connected in a series circuit path, including a capacitor, across an AC source for charging the capacitor, and a secondary winding connected in series with a pair of ignition electrodes positioned adjacent a fuel outlet; a normally non-conducting silicon controlled rectifier, connected in shunt with the primary winding and the capacitor, is rendered conductive permitting the capacitor to discharge through the primary winding producing a voltage in the secondary winding whereby an ignition spark is generated across the electrodes for igniting the fuel; a control circuit enabled when the fuel is ignited inhibits further operation of the silicon control rectifier and thus inhibits further spark generation.

United States Patent '91 Matthews [s41 AUTOMATIC FUEL IGNITION SYSTEM [75] lnventor: Russell B. Matthews, Goshen, Ind.

[73] Assigneez' Johnson Service Company, Milwaukee, Wis.

[ 22] Filed: Sept. 7,1971

21] Appl. No.: 173,019

52 U.S.Cl. ..43l/2t54,317/96 51 Int. cl. ..-.F23q 3 00 [58] FieldofSearch ..43l/74,264,69,70,71,25;

['56] k References Cited UNITED STATES PATENTS 3,384,440 3,405,993 10/1968 Walbridge ..4a1/2s 5/1968 Mayeriului ..431/"/4x 1 3,718,423 1 Feb. 27,- 1973 Primary Examiner-Edward G. Favors Attorney-John A. Dienner et al.

[57] ABSTRACT v An automatic fuel ignition system includes an ignition circuit having an ignition transformer with a primary winding connected in a series circuit path, including a capacitor, across an AC source for charging the v capacitor, and a secondary winding connected in seties with a pair of ignition electrodes positioned adjacent a fuel outlet; a normally non-conducting silicon controlled rectifier, connected in shunt with the primary winding and the capacitor, is rendered conductive permitting the capacitor to discharge through the primary winding producing a voltage in the secondary winding whereby an ignition spark is generated across the electrodes for igniting the fuel; a control. circuit enabled when the fuel is ignited inhibits further operation of the silicon control rectifier'and thus inhibits further spark generation.

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AUTOMATIC FUEL IGNITION SYSTEM BACKGROUND or THE INVENT ON 1. Field of the Invention The present invention relates to electronic fuel ignition systems, and more particularly to a system for automatically providing iginition and reignition of a gaseous fuel..

2. Description of the Prior Art One known fuel ignition system which provides automatic ignition and reignition of a gaseous fuel is disclosed in the U.S. Pat. No. 3,377,125 of Robert J. Zielinski. The system employs an ignition transformer having a primary winding and a secondary winding and relaxation oscillator means for producing a pulse of current through the primary winding of the ignition transformer for each cycle in which operation of the relaxation oscillator is initiated.

The secondary winding of the ignition transformer is connected in circuit with a pair of ignition electrodes. Each time a current pulse is provided in the primary winding, a corresponding voltage pulse is produced in the secondary winding'which voltage pulse is applied to the ignition electrodes ,togenerate ignition sparks in the region in which a gas flame is to be produced. In accordance with one disclosed embodiment, the ignition circuit yields one spark' approximately every 0.6 second. i I The'relaxation oscillator includes a normally'nonconducting silicon controlled rectifier having an anodecathode circuit connected in a series circuit with the primary winding the ignition transformer across a d.c. source. A first capacitor having a predetermined charging time constant is connected in parallel with the series circuit. The first capacitor is charged from the dc. source wheneverthe SCR is non-conducting. A second capacitor having a charging time constant that is greater than that of the first capacitor is also charged from the d'.c. source for effecting turnon of the silicon controlled rectifier when .the second capacitor has charged to a selected voltage. The turnon of the silicon A controlled switching device, such as a normally voltage. During the alternate half cycles, the line voltcontrolled rectifier enables the first capacitor to discharge through the series circuit including the primary winding, thereby effecting the generation of an ignition spark at the ignition electrodes for igniting the gaseous fuel. When the gas is ignited, the presence of a flame between the ignition electrodes, will prevent the second capacitor from charging to the voltage level that is required to turnon the silicon controlled rectifier, and thus the sparking will cease. Upon extinction of the flame, spark generation will begin'approximately one second after the flame-is out.

I SUMMARY OF THE INVENTION The present invention provides an improved automatic fuel ignition system which minimizes the time required for ignition or reignition of a gaseous fuel. in accordance with one embodiment, the fuel ignition system providedby the, present invention comprises an ignition circuit including an ignition transformer having AC line voltage. v

age is conducted over a path to switch the silicon controlled rectifier to a conducting state, thereby providing a discharge path for the capacitor through the primary winding of the ignition transformer. When the capacitor discharges, a current pulse conducted through the primary winding of the ignition transformer produces a voltage pulse in the secondary winding of the transformer.

The secondary winding of the ignition transformer is connected in series with a pair of ignition electrodes and a control circuit, and the voltage pulses produced in the secondary winding are applied to the ignition electrodes to generate sparks in the region in which a flame is to be produced.

When the fuel is ignited, the resistance between the ignition electrodes decreases, enabling the control circuit to inhibit further switching of the silicon. controlled rectifier to thereby stop further sparking as long as the flame remains lit. If the flame should inadvertently be extinguished, the control circuit will be disabled, permitting the silicon controlled rectifier to be controlled byv the line voltage and sparking will commence inapproximately one half cycle of the line voltage.

The spark producing capability of the ignition circuit is a "function of the frequency of the energizing line voltage, and accordingly for a 60 Hertz line signal, the exemplary embodiment of theignition circuit produces sparks at the rate of sixty sparks per second until the fuel is ignited. Moreover, should the flame become temporarily extinguished, such as by flame-out, or a sudden interruption in the fuel supply the ignition circuit will begin to produce ignition sparks within approximately 0.03 seconds after the flame disappears.

This improved ignition spark generation rate is achieved by controlling the turnon of the silicon controlled rectifier directly by the line voltage rather than through the use of a time dependent network such as is shown by Zielinski. The increased number of sparks provided during each second, which is over sixty times greater than the numberprovided by the prior art circuit and the reduction in the time delay between flame-out and the generation of ignition sparks provides for more rapid ignition of the fuel thereby minimizing the amount of unburned gases which might otherwise accumulate.

Furthennore, since the silicon controlled rectifier is connected in shunt with the primary winding of the ignition transformer rather than in series with the winding as shown in the prior art, the silicon controlled rectifier is less susceptible to damage as may be caused by improper connections of the ignition circuit to the line voltage source.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to thesingle-FIGURE which comprises the only drawing of the disclosure, the automatic fuel ignition comprises an ignition circuit 20 which includes an ignition transformer Tl for applying voltages between a pair of ignition electrodes 21, 22 to ignite a gaseous fuel emanating from the outlet 26 of a conduit 23 of a gas burner apparatus 24. The gas burner 24 may in clude a regulating valve 25 for controlling the flow of gas through the conduit 23. One of the electrodes 21 is connected to the secondary winding 36 of the ignition transformer and the second electrode 22 is connected to ground, or to the conduit 23 of the gas burner 24.

Alternatively, the conduit 23 which is grounded may serve as the grounded electrode 22.

The ignition circuit 20 has a pair of input leads 30 and 31 connected to an A.C. voltage source which may be a standard 60 Hertz, 120 volt A.C. line voltage source. A resistor R1, a diode DI, the primary winding 32 of the ignition transformer TI, a capacitor CI and a second diode D2 are connected in a series circuit between the line conductors 30 and 31 providing a unidirectional circuit path for charging capacitor Cl to a predetermined voltage whenever the voltage on line 30 is positive with respect to line 31.

A controlled switching device, embodied in the exemplary example as a silicon controlled rectifier SCRI, has an anode-cathode circuit connected between junction points 33 and 34 in shunt with the primary winding 32 of the ignition transformer and the capacitor Cl. The silicon controlled rectifier which is normally nonconducting, provides a normally open shunt circuit permitting capacitor CI to charge whenever line 30 is positive with respect to line 31. I

A capacitor C2 is connected between the cathode of the silicon controlled rectifier SCRI and line conductor 31. The gate of the silicon controlled rectifier SCRIis connected over a resistor R2 to line conductor 31.

A pair of resistors R3 and R4 are connected in series across conductors 30 and 31. The junction of the resistors R3 and R4 is connected to the cathode of the silicon controlled rectifier at junction 34. Whenever the voltage on line 31 is positive with respect to line 30 current flow over the unidirectional current path is blocked by diodes DI and D2, and thus current flows over resistors R3 and R4 from line 31 to line 30.

The resultant voltage drop across resistor R4 provides a potential at the cathode of the silicon controlled rectifier SCRI relative to the gate of the silicon controlled rectifier' sufficient to trigger the silicon controlled rectifier SCRI into conduction. Consequently, a shunt circuit path is provided across the series connected primary winding 32 of ignition-transformer TI permitting the capacitor CI to discharge through the primary winding 32 and the anode-cathode circuit of the silicon controlled rectifier SCRI.

The secondary winding 36 of the ignition transformer TI has one end 37 connected to the ungrounded ignition electrode 21, and a second end 38 connected over isolation capacitor C4 to line 30 and to a control circuit 40 "which includes a transistor QI. The base of transistor QIis connected over a resistor R and a diode D3 to end 38 of, the secondary winding and over capacitor C3 to conductor 31. The collector of the transistor 01 is connected to the, cathode of the silicon controlled rectifier SCRI at junction 34.The emitter of transistor 01 is connecteddirectly to line conductor 31.

-OPER ATION OF THE IGNITION CIRCUIT For purposes of illustration of the operation of the automatic fuel ignition circuit provided by the present invention, it is assumed that the'ignition circuit is energized with the silicon controlled rectifier SCRI nonthe applied AC voltage, current from the AC source flows through resistor RI, diode DI and the primary winding 32 of ignition transformer TI to charge capacitor CI and through diode D2 to the line conductor 31.

During the next half cycle of the applied A.C. voltage, line conductor 31 will become positive with respect to line conductor and current will flow from line conductor 31 through resistors R4 and R3 to line conductor 30. The voltage drop across resistorR4 is sufficient to trigger the silicon controlled rectifier SCRI t0 conduction. When the silicon controlled rectifier SCRI is rendered conducting, capacitor CI discharges through the primary winding 32 of ignition transformer TI and the anode-cathode circuit of the silicon controlled rectifier SCRI which is connected in parallel with the primary winding 32. and capacitor CI. The discharge of capacitor C1 through the primary winding 32 provides a current pulse in the primary winding 32. This current pulse in turn produces a voltage pulse in the secondary winding 36 of the ignition transformer TI, which is applied to the ignition electrodes 21 and 22, generating a spark across electrodes 21 and 22. The spark gap provided by the electrodes is placed in the region adjacent the outlet 26 of the conduit 22. vAccordingly, when the gas flow control valve 25 is open and gas is emanating from the conduit 23, the sparks generated will ignite the gas.

The ignition sequence with capacitor C1 being charged and discharged during alternate half cycles of the power signal will continue, providingsparks between the electrodes 21 and 22 at the rate of sixty sparks per second until the gas is ignited.

When a flame is present between the electrodes21 and 22, the resistance between the electrodes decreases. Accordingly, whenthe gas has been ignited, and as line conductor 31 again becomes positive with respect to line conductor 30, current from the A.C. source will flow from the conductor 31 through capacitor C3, resistor R5, diode D3, the secondary winding 36 of the ignition transformer T1 to electrode 21, and through the flame to electrode 22 which is connected to ground. This current flow produces a voltage across capacitor C3 causing the base of transistor QI to become positive with respect to emitter of transistor QI, driving transistor QI into saturation. Consequently, transistor 01 through its emitter-collector circuit, effectively short-circuits the gate to cathode circuit of the SCRI, causing SCRI to be turned off.

Transistor 01 will remain conducting as long as the flame remains lit such that the silicon controlled rectifier SCRI will not be triggered into conduction and capacitor CI will not discharge. Thus, when the flame is lit, the control circuit 40 will inhibit the generation of sparks between electrodes 21 and 22. 7

If the pilot flame suddenly becomes extinguished, such as by flame-out or sudden interruption in the gas supply, the impedance of the charging path for capacitor C3 will increase to a value where capacitor C3 will discharge and transistor Q will be cut off. Under such conditions, silicon controlled rectifier SCRl will again conduct during alternate half cycles of the applied voltage to permit capacitor C1 to discharge thereby effecting the generation of sparking between electrodes 21 and 22 to reestablish the flame.

In one exemplary embodiment, the circuit components may have the following values:

Resistor RI 1000 ohms Resistor R2 100 ohms I Resistor R3 680K ohms Resistor R4 6800 ohms Resistor R5. l0 megohms Capacitor Cl 1 microt'arad Capacitor C2 0.47 microfarads Capacitor CS 0.0! microfarads Capacitor C4 680 micromicrofarads Diodes Di, D2, D3 Silicon Control Rectifier SCRl CIOGB Transistor Ql 2N5355 Transformer TI The foregoing values are provided to illustrate one embodiment for the fuel ignition circuit provided by the present invention and are not intended as a limitation v of true scope of the invention.

Iclaim:

1. In an automatic fuel ignition system for providing electronic ignition of gas emanating from gas burner apparatus, an ignition circuit including an ignition transformer having a primary winding and a secondary winding,'capacitor means, means connecting said primary winding and said capacitor means in a series 'unidirectionalcurrent path across a source of cyclical A.C. ,voltage for charging said capacitor means to a predetermined voltage during each first half cycle of the A.C. voltage, switching means responsive to each second half cycle of the A.C. voltage for causing discharge of said capacitor means through said primary winding for producinga pulse of current through said primary winding, a pair of ignition electrodes spaced apart to provide a gap therebetween and connected in a series circuit with said secondary winding whereby an ignition spark is generated between said electrodes whenever a pulse of current is provided in said primary winding, said electrodes being positioned so that ignition sparks between said electrodes will ignite gas from said gas burner apparatus to provide a flame which bridges'the gap between said electrodes, and control means enabled whenever a flame bridges the gap between said electrodes to inhibit said'switching means thereby preventing the discharge of said capacitor means and the generation of ignition sparks.

2. An automatic fuel ignition system as set forth'in claim 1' whereinsaid switching means includes a controlled switching device having a pair of electrodes connected in a shunt circuit path across said capacitor means and said primary winding and a control electrode connected to a point of reference voltage, and means for rendering said switching device conductive between the electrodes of said pair during said second half cycle of the A.C. voltage to provide a discharge path for said capacitor means over said primary winding and said pair of electrodes of said device.

3. An automatic fuel ignition system as set forth in claim 2 wherein said control means includes a transistor having an output circuit connected to an electrode of said controlled switching device and a control electrode, and circuit means connectedin series with said secondary winding and said ignition electrodes for providing a control voltage over said control electrode whenever a flame bridges said ignition electrodes for enabling said transistor to extend a disabling potential to one electrode of said controlled switching device to maintain said device non-conductive.

4. In an automatic fuel ignition system for providing electronic ignition of gas emanating from gas burner apparatus, an ignition circuit including an ignition transformer having a primary winding and a secondary winding, charging path means including capacitor means and said primary winding connected across an A.C. voltage source for charging said capacitor means to a predetermined voltage, a normally turned off silicon controlled rectifier having an anode-cathode circuit connected in shunt with said primary winding and said capacitor means, means for effecting the turnon of said silicon controlled rectifier after said capacitor means is charged to said predetermined voltage, enabling said capacitor means to discharge through said primary winding and the anode-cathode circuit of said silicon controlled rectifier thereby providing a pulse of current through said primary winding, a pair of ignition electrodes spaced apart to provide a gap therebetween and connected in a series circuit with said secondary winding whereby an ignition spark is generated between said ignition electrodeswhenever a pulse of current is provided in said primary winding, said ignition electrodes being positioned so that ignition sparks between said electrodes will ignite gas from said gas burner apparatus to provide a flame which bridges the gap between said electrodes, and control means enabled whenever a flame bridges the gap between said electrodes to inhibit turnon of said silicon controlled rectifier thereby preventing the discharge of said capacitor means and the generation of ignition sparks. 

1. In an automatic fuel ignition system for providing electronic ignition of gas emanating from gas burner apparatus, an ignition circuit including an ignition transformer having a primary winding and a secondary winding, capacitor means, means connecting said primary winding and said capacitor means in a series unidirectional current path across a source of cyclical A.C. voltage for charging said capacitor means to a predetermined voltage during each first half cycle of the A.C. voltage, switching means responsive to each second half cycle of the A.C. voltage for causing discharge of said capacitor means through said primary winding for producing a pulse of current through said primary winding, a pair of ignition electrodes spaced apart to provide a gap therebetween and connected in a series circuit with said secondary winding whereby an ignition spark is generated between said electrodes whenever a pulse of current is provided in said primary winding, said electrodes being positioned so that ignition sparks between said electrodes will ignite gas from said gas burner apparatus to provide a flame which bridges the gap between said electrodes, and control means enabled whenever a flame bridges the gap between said electrodes to inhibit said switching means thereby preventing the discharge of said capacitor means and the generation of ignition sparks.
 2. An automatic fuel ignition system as set forth in claim 1 wherein said switching means includes a controlled switching device having a pair of electrodes connected in a shunt circuit path across said capacitor means and said primary winding and a control electrode connected to a point of reference voltage, and means for rendering said switching device conductive between the electrodes of said pair during said second half cycle of the A.C. voltage to provide a discharge path for said capacitor means over said primary winding and said pair of electrodes of said device.
 3. An automatic fuel ignition system as set forth in claim 2 wherein said control means includes a transistor having an output circuit connected to an electrode of said controlled switching device and a control electrode, and circuit means connected in series with said secondary winding and said ignition electrodes for providing a control voltage over said control electrode whenever a flame bridges said ignition electrodes for enabling said transistor to extend a disabling potential to one electrode of said controlled switching device to maintain said device non-conductive.
 4. In an automatic fuel ignition system for providing electronic ignition of gas emanating from gas burner apparatus, an ignition circuit including an ignition transformer having a primary winding and a secondary winding, charging path means including capacitor means and said primary winding connected across an A.C. voltage source for charging said capacitor means to a predetermined voltage, a normally turned off silicon controlled rectifier having an anode-cathode circuit connected in shunt with said primary winding and said capacitor means, means for effecting the turnon of said silicon controlled rectifier after said capacitor means is charged to said predetermined voltage, enabling said capacitor means to discharge through said primary winding and the anode-cathode circuit of said silicon controlled rectifier thereby providing a pulse of current through said primary winding, a pair of ignition electrodes spaced apart to provide a gap therebetween and connected in a series circuit with said secondary winding whereby an ignition spark is generated between said ignition electrodes whenever a pulse of current is provided in said primary winding, said ignition electrodes being positioned so that ignition sparks between said electrodes will ignite gas from said gas burner apparatus to provide a flame which bridges the gap between said electrodes, and control means enabled whenever a flame bridges the gap between said electrodes to inhibit turnon of said silicon controlled rectifier thereby preventing the discharge of said capacitor means and the generation of ignition sparks. 